The Evolved Packet System (EPS) of the 3rd Generation Partnership Project (3GPP) consists of Evolved Universal Terrestrial Radio Access Networks (E-UTRAN), Mobility Management Entities (MME), Serving Gateways (S-GW), Packet Data Network Gateways (P-GW) and Home Subscriber Servers (HSS), as shown in FIG. 1.
The MME is responsible for control plane related work, such as mobility management, processing of non-access layer signaling and management of user mobility management context. The S-GW, which is an access gateway device connected to the E-UTRAN, transfers data between the E-UTRAN and the P-GW and is responsible for caching paging data. The P-GW, which is a boundary gateway between the EPS and the packet data network (PDN), is responsible for access of the PDN, transferring data between the EPS and the PDN, etc. The UE might also access to the upgraded SGSN through the UTRAN, and then the SGSN accesses to packet services by a connection the P-GW and the S-GW. This upgraded SGSN is called as an S4 SGSN. It executes control plane interaction with the MME via the S3 interface and executes user plane interaction with the S-GW via the S4 interface.
Provided that the EPS system supports the Policy and Charging Control (PCC), a Policy and Charging Rules Function (PCRF) entity makes policy and charging rules, and is connected to an Application Function (AF) entity in an operator's Internet Protocol (IP) service network via the Rx interface to acquire service information, so as to generate the service information of the PCC strategy. When the GTP protocol is used in the S5 interface between the S-GW and the P-GW, a Policy and Charging Enforcement Function (PCEF) entity resides in the P-GW. The PCRF entity exchanges information with the P-GW via the Gx interface and is responsible for initiating establishment, modification and release of a bearer to ensure the quality of service (QoS for short) of service data and perform charging control. When the Proxy Mobile IP (PMIP) is used in the S5 interface between the S-GW and the P-GW, a Bearer Binding and Event Report Function (BBERF) entity resides in the S-GW, information is exchanged between the S-GW and the PCRF entity via the Gxc interface, the BBERF entity is responsible for initiating the establishment, modification and release of the bearer to ensure the QoS of the service data, and the PCEF entity performs the charging control.
The EPS system supports online charging and offline charging of the corresponding user. For the online charging, the P-GW interacts with an Online Charging System (OCS) via the Gy interface, and implements the credit control and management. For the offline charging, the P-GW interacts with the Offline Charging System (OFCS) via the Gz interface and reports billing information.
For the online charging, during the implementation of the credit control and management, the OCS provides credit authorization for services accessed by the user according to the user subscription and the operator's strategy and sends a re-authorization trigger for the P-GW to re-request the credit. For example, the P-GW must re-request the credit from the OCS when the SGSN serving the UE changes.
Then, in a frame shown in FIG. 1, when the PMIP protocol is used between the S-GW and the P-GW, the P-GW is unaware of the change of the SGSN such that the P-GW cannot re-request the credit from the OCS.
The same problem also exists in an EPS home route roaming scenario shown in FIG. 2 and an EPS local breakout roaming scenario shown in FIG. 3, in which the P-GW is also unaware of the change of the SGSN such that the P-GW cannot re-request the credit from the OCS.